This invention relates to snare devices, and more particularly to endovascular snaring instruments.
A clot in a patient""s blood vessel poses grave risks for those portions of a patient""s anatomy that are downstream from the clot. Because a clot can inhibit blood flow, cells that rely for their nourishment on blood passing through the obstructed vessel can die. If those cells are particularly essential to life, such as cells associated with the brain or the heart, the patient can also die.
When a blood clot is small relative to the blood vessel, or where the clot is obstructing a relatively minor blood vessel, the patient is generally in no immediate danger. Nevertheless, there does exist the more insidious danger of the blood clot becoming detached and coming to rest again in another blood vessel in which its obstructive effect is less benign. Additionally, there exists the danger that small blood clots migrating through the circulatory system will coalesce with a stationary clot and thereby cause it to enlarge by accretion. When this occurs, a clot of negligible size can grow into a significant obstruction. This growth can occur rapidly because as the clot grows, it introduces more turbulence into the blood flow. This turbulence tends to break up thrombocytes as they pass through the turbulent zone, thereby causing additional clotting.
Conventional methods of removing a blood clot rely on the introduction of medicaments, such as enzymes, that dissolve blood clots. Because the enzymes, such as streptokinase, are introduced into the bloodstream, their effects are systemic rather than local. In addition, the process of dissolving a clot is a time-consuming one during which the patient continues to be in some danger.
Mechanical methods of removing a blood clot have been generally unsuccessful because of the fragility of the clot. When disturbed by a conventional mechanical device, a clot can easily fragment into smaller clots, each of which then begins migrating through the blood stream before settling at an unpredictable location.
The invention is based on the recognition that when one pulls on a wire, different sections of the wire can be made to stretch by different amounts. This phenomenon is advantageously applied in a surgical instrument having a distal end that readily transitions from an extended state to a coiled state. In the extended state, the instrument can be slipped into an extremely small space, such as the space between a blood clot and the wall of a vessel, without disturbing the clot. In the coiled state, the instrument can ensnare the clot.
In general, the invention features surgical and other instruments that include a longitudinally-extending support member that defines an axis. The support member includes a flexible distal section and a rigid proximal section. The flexible distal section has an equilibrium compressed state and a non-equilibrium uncompressed state. In its compressed state, the flexible distal section defines a first path relative to the axis.
The instruments further include a core-wire that extends along the axis defined by the support member. The core-wire has a relaxed state and a tensioned state. In its relaxed state, the core wire defines a second path relative to the axis. An actuator coupled to the core-wire enables a user, such as a surgeon, to apply a tensile force that pulls on the core-wire. This tensile force places the core-wire under tension and thereby causes it to transition from its relaxed state, in which the flexible distal section is in its uncompressed state, to its tensioned state, in which the flexible distal section is in its equilibrium compressed state.
The distal section of the support member includes an anchor to which the core-wire is attached. This anchor, which can be at any point along the distal section of the support member, provides a mechanical coupling that enables the flexible distal section of the support member to follow one of the first path, as defined by the flexible distal section in its compressed state, and the second path, as defined by the core-wire in its relaxed state.
The core-wire has a distal section having a first yield force and a proximal section having a significantly higher yield force. In one embodiment, the core-wire is made of a super-elastic and shaped-memory metal. In this embodiment, the difference in yield forces is achieved by providing a proximal section with a first cross-sectional area and a distal section with a second cross-sectional area that is smaller than the first cross-sectional area. The distal section of the core-wire is made to have a relaxed state in which it traces a substantially helical or coiled path. The flexible distal section of the support member is made to have a compressed state in which it traces a path substantially parallel to the axis of the support member.
Because the two sections of the core-wire have two different cross-sectional areas, a given force exerted by the user results in more stress in the distal section of the core-wire than it does in the proximal section of the core-wire. This results in the distal section experiencing more strain, and hence greater elongation, than the proximal section. Because the distal section of the core-wire is anchored to the distal section of the support member, the additional length of the core-wire enables the flexible distal section of the support member to revert to its equilibrium compressed state, in which it extends in a direction substantially parallel to the axis of the support member.
Other methods exist of providing a core-wire having sections with different yield strengths. For example, a core-wire can be made of two dissimilar materials having different yield strengths. Or a core-wire can be locally heat-treated to change the yield stress in the heat-treated region.
To ensnare a blood clot, kidney stone, or other object, the surgeon first pulls on the core-wire. This elongates the distal section of the core-wire and hence enables the flexible distal-section of the support member to revert to its compressed state. In this compressed state, the flexible distal-section of the support member defines a line substantially parallel to the axis of the support member. The surgeon then slips the distal-section between the clot and the wall of the blood vessel so that the distal-section of the support member is adjacent to the clot.
Once the distal section of the support member is adjacent to the clot, the surgeon releases the core-wire, thereby restoring the core-wire to its coiled state. This causes the distal section of the support member to also assume a coiled state, and to thereby ensnare the clot alongside it.
The surgical instruments of the invention enable the surgeon to capture a clot and remove it from the blood vessel. In its relaxed state, the flexible distal-section gently cradles the clot within its coils. Since the instrument never penetrates the clot during the removal procedure, the integrity of the clot remains undisturbed. As a result, there is little likelihood that the clot, despite its fragility, will fragment as it is removed. The surgical instruments of the invention thus provide a reliable alternative to the use of systemic medicaments that slowly dissolve a clot.
Instruments embodying the principles of the invention can be used in applications other than the removal of a clot. For example, such instruments can be used to ensnare and remove gall stones. In addition, such instruments can be slipped by a kidney stone and formed into a basket, or strainer, between the kidney stone and the kidney. This basket can then be used to capture and remove kidney stone fragments during lithotripsy. Surgical instruments according to the invention can also be deployed as temporary stents in a blood vessel that has been constricted due to a vasospasm. In this application, the surgeon places the distal end of the support member into its extended state and slips it through the constricted section of the blood vessel. The surgeon then restores the distal end to its coiled state, in which the coils of the distal end dilate the blood vessel and restore blood flow.
Instruments embodying the invention can also be used in non-surgical applications. In particular, such instruments can be used in any application in which it is necessary to ensnare and retrieve an object that is lodged in an inaccessible space. For example, such instruments can be designed to remove clogs from plumbing fixtures or foreign objects from pipes, for example in a food-processing plant, without the need to dismantle the pipes.
In other embodiments, pairs of instruments can be used together to perform tasks that would be difficult to achieve with only a single instrument. For example, to remove a blood clot that is on the other side of a constricted section of a blood vessel, a first instrument can be deployed as a temporary stent while a second instrument retrieves the blood clot after passing through the helix formed by the coils of the first instrument. A first instrument can also be deployed as a basket between a particularly delicate blood clot and the heart, while a second instrument ensnares and removes the blood clot. Any fragments of the blood clot are then captured and removed by the first instrument.
As used herein, the terms xe2x80x9crigidxe2x80x9d means sufficiently incompressible so as to retain its form when subjected to tensile and compressive forces but nevertheless able to bend sufficiently to negotiate to negotiate twists and turns in the vasculature or other flow system in which it is to be deployed.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
The present invention thus offers the advantage of providing safe and rapid removal of obstructions disposed in difficult to access regions. By ensnaring rather than piercing such obstructions, the invention enables the removal of even fragile obstructions without a significant danger of fragmenting those obstructions.
The present invention further provides a temporary stent that can open up a constricted flow channels and restore flow therethrough, even when the constricted flow channel is relatively inaccessible.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.